Type- DESCRIBE table_name;
*NOTE: Your Oracle user and/or schema must have permissions/privaliages or be within the schema to describe the table.
You can use the data_dictionary views to get the table info.

the ampersand operator is used to take the input at runtime( ex:-&employeename) and if ampersand is used twice i.e && then it will take the input of single ampersand operator and is used to provide data to the query at runtime.